Editing Spontaneous parametric down-conversion (section)

{{Short description|Optical process}}
[[Image:Spontaneous Parametric Downconversion.png|thumb|350px|Schematic of SPDC process. Note that conservation laws are with respect to energy and momentum ''inside'' the crystal.]]
'''Spontaneous parametric down-conversion''' (also known as '''SPDC''', '''parametric fluorescence''' or '''parametric scattering''') is a nonlinear instant optical process that converts one photon of higher energy (namely, a ''pump'' photon) into a pair of photons (namely, ''signal'' and ''idler'' photons) of lower energy, in accordance with the laws of [[law of conservation of energy|energy conservation]] and [[law of conservation of momentum|momentum conservation]]. It is an important process in [[quantum optics]], for the generation of [[photon entanglement|entangled photon]] pairs and of single photons.